Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR DETERMINING
DOCUMENT AUTHENTICITY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to methods and apparatus for
analyzing documents. This invention more specifically relates to methods and
apparatus for verifying the authenticity of a document by processing and
analyzing
reflected light which is collected from the document.
2. Backeround Information
Devices have been known for testing the presence of color in paper
securities, for checking bank notes, for validating currency, for optical
recognition of
patterns on documents, and for generally distinguishing between authentic and
counterfeit documents. It has been known to provide such devices in various
ways.
U.S. Patent No. 4,183,665 provides a device for determining whether a
document has color in it. Filters for this device are chosen to detect if a
specific color
is present on the document in question. Verification of authenticity for this
device
requires the personal judgment of the user as to which colors are present on
the
document.
U.S. Patent No. 5,537,486 teaches a device which is stated to be a
high-speed document verification system. It is primarily designed to detect
fine
patterns which may not be reproduced by copying equipment.
U.S. Patent No. 4,204,765 teaches an apparatus for testing colored
securities. This device uses different colored diodes for illumination to
determine if
color is present in a tested document.
U.S. Patent No. 4,184,081 teaches a method for checking banknotes
and apparatus therefor. This patent provides an instrument for measuring color
which
initiates its analysis on the premise that the color of the copy will not
appear exactly
the same as the color of the original.
U.S. Patent No. 4,319,137 teaches an apparatus for identifying sheet-
like printed matters. The device of this patent is directed to black and white
pattern
recognition.
CA 02384112 2005-10-04
U.S. Patent No. 4,587,434 is provided as a currency note validator. This
device utilizes a narrow band LED illumination to measure responses of a
currency note to a
specific portion of the spectrum.
U.S. Patent No. 3,679,314 teaches an apparatus for optically testing the
genuineness of banknotes and other tokens of value. This device uses several
narrow band
light sources and receives and analyzes the light that is transmitted through
the document.
U.S. Patent No. 3,220,540 teaches a method and apparatus for discriminating
between "desired" and "undesired" documents. This device uses several narrow
band light
sources and takes measurements on several areas of a target document.
U.S. Patent No. 3,480,785 provides a method and apparatus for validating
documents by spectral analysis of light reflected therefrom. This device
employs a
comparison of measured values in relationship to each other for validation.
U.S. Patent No. 5,027,415 is provided as a bill discriminating device which
uses two narrow band detectors and a ratio comparison of values measured in
testing to
verify the authenticity of documents tested.
U.S. Patent No. 4,618,257 is a colour sensitive currency verifier which uses
two sensors augmented with filters to analyze narrow band width spectral
readings on a
target. Validation of authenticity occurs by comparison of the difference
between the two
2 0 measurements.
U.S. Patent No. 5,498,879 teaches an apparatus for optical recognition of
documents by photoelectric elements having vision angles with different length
and width.
This device uses several narrow band sensors over a linear strip of the
document to measure
different reflective values of the light in those particular areas.
2 5 U.S. Patent No. 4,204,765 discloses an apparatus for testing colour
securities. This device uses narrow band light sources to provide reflective
light.
Humans are considered to have a tristimulus system, which means that they
have three types of colour sensors which are sensitive to different weighted
portions of the
visible spectrum. However, the exact mechanism for colour vision is not
completely
3 0 understood due to the difficulty of analyzing the effects of the neural
network of the brain as
these effects relate to the retina-brain connection. In lieu
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of the exact mechanism of color perception, a set of weighting functions was
derived
from a color matching experiment and adopted as a standard observer by
Commission
Internationale de 1'Eclairage (CIE). Three spectral weighting functions in
particular
comprise the tristimulus CIE standard observer, which can be employed as a
model of
human color perception.
A person is generally unaware of these three individual responses to a
color object, and instead senses a composite effect of the three stimuli. This
behavior
of human color perception permits different spectral distributions to appear
identical
to a human observer. For example, a broad spectrum of light reflected from an
object
may be interpreted by a human visual system to be white, but the proper blend
of red,
blue, and green colors will also appear white to the human observer. These two
spectrums have different spectral compositions, but they both may be perceived
by a
human observer to have identical color appearances. Unfortunately, this error
in
judgment is a boon to those who illegally profit from the reproduction of
certain
documents such as currency.
Conventional production techniques can produce a first document
which has colors which appear to a human observer to be the same as the colors
in a
second, similar document. However, if the same coloring process was not
employed
to produce these documents, then the documents are susceptible to
differentiation. To
a human observer, though, the colors of the first document can appear
identical to the
colors of the second document. Employing broadband spectral analysis can
demonstrate the differences in the colors of these documents.
Conventional use of spectral analysis has been limited to devices
which utilize relatively narrow color bands to differentiate between authentic
documents and their counterpart reproductions. As a result, an apparatus and
method
are needed which can be applied for broadband spectral analysis on a wide
variety of
documents.
What is needed then is a document authentication method and
apparatus which use a light source to obtain a broad spectrum of reflected
light from a
document. A more effective and thorough normalizing of the light analyzed is
also
needed to verify the authenticity of a variety of documents. In addition, a
consistently
3
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accurate method and apparatus for comparing the spectral signature generated
by a test
document to a previously programmed target document is needed.
SUMMARY OF THE INVENTION
The exemplary method and apparatus for verifying authenticity of a
document according to aspects of the present invention can satisfy the above-
mentioned
needs as well as others.
According to an aspect of the present invention, there is provided a method
for determining the authenticity of a document comprising: providing a
broadband light
source; illuminating at least a portion of the document with the broadband
light source to
produce a broadband spectrum of reflected light from the document; collecting
the
broadband spectrum of reflected light: converting the broadband spectrum of
reflected light
into at least one electrical signal corresponding to the broadband spectrum of
reflected light;
generating an intensity value for each of a plurality of different wavelengths
of light in the
broadband spectrum of reflected light; digitizing the electrical signals of
the broadband
spectrum of reflected light; producing a spectral signature that includes an
array of the
intensity values; and comparing the array of intensity values of the spectral
signature with
an array of reference intensity values of a reference spectral signature to
determine the
authenticity for the document.
2 0 According to a further aspect of the present invention, there is provided
an
apparatus for authenticating a document comprising: means for providing a
broadband light
source; means for illuminating at least a portion of a document with the
broadband light
source to produce a broadband spectrum of reflected light from the document;
means for
collecting the broadband spectrum of reflected light; means for converting the
broadband
2 5 spectrum of reflected light into at least one electrical signal
corresponding to the broadband
spectrum of reflected light; means for generating an intensity value for each
of a plurality of
different wavelengths of light in the broadband spectrum of reflected light;
means for
digitizing the electrical signals of the broadband spectrum of reflected
light; means for
producing a spectral signature that includes an array of the intensity values
of the document;
3 0 and means for comparing the array of intensity values of the spectral
signature with an array
of reference intensity values of a reference spectral signature to determine
an authenticity
for the document.
4
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A method is disclosed which provides the initial step of providing a
broadband light source and illuminating a portion of a document to be verified
with the
broadband light source. This generates reflected light from the document. The
method then
provides for collecting and analyzing the reflected light by converting it
into a
corresponding electrical signals or signals. Next, the electrical signal or
signals are
digitized to form an array. The method can then include normalizing this array
to develop
and store a spectral signature associated with the document. The method then
provides for
comparing a test document spectral signature to the spectral signature of a
previously stored
document. This comparison of the test document spectral signature to the
previously stored
spectral signature can be accomplished by using a matching function to
determine
authenticity.
An apparatus is also disclosed which may include an enclosure having a
transparent opening disposed therein. A broadband light source is provided to
illuminate a
portion of a document placed on the transparent opening. The apparatus may
employ a
collection lens and optical fiber to receive and transfer light received from
the illuminated
document. This reflected light is then transferred to an aperture which is
located at the focal
point of a collimating lens. The collimating lens functions in conjunction
with a diffraction
grating, or another suitable spectral spreading device, to provide a spectrum
of light
2 0 wavelengths to a photosensor device. A microcontroller or conventional
microprocessor
and additional components can then be employed in conjunction with the
apparatus to
perform storage and authenticity determination functions for tested documents.
In another
aspect of the present invention, several steps of the process may be condensed
into the
functionality of a single optical component.
2 5 Accordingly, it is desirable to provide a document analysis method and
apparatus which utilize a broader range of wavelengths to provide a more
thorough analysis
in determining document authenticity.
It is further desirable to provide an apparatus which may be produced at an
economical cost.
3 0 It is also desirable to provide a document analysis method and apparatus
which reduce the inherent variation introduced into the analysis by soiled or
faded
documents which are tested.
CA 02384112 2005-10-04
These and other features and advantages of the invention will be more fully
understood from the following description on reference to the illustrations
appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a process flow diagram of the preferred method of the present
invention;
Figure 2 is a graph of an embodiment of authentication output for the present
invention;
Figure 3 is a schematic view of a typical embodiment of the apparatus of the
present invention; and,
Figure 4 is a partially schematic top isometric view of an embodiment of the
apparatus of the present invention with its cover removed.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term "document" is defined in its ordinary sense and
includes documents such as, but not limited to, currency, paper checks, bank
checks, bank
drafts, lottery tickets, coupons, event tickets, stock certificates, bonds,
bearer instruments
and similar documents which provide some benefit to the holder or are
otherwise worth
2 0 counterfeiting.
In the context of the present invention, the term "authenticity" means that a
document is consistent with some target value or within a range including some
target
value.
Sa
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The term "broadband" as used herein refers to light wavelengths within
the visible range of light as well as those in the infrared and ultraviolet
portions of the
spectrum.
The terms "array" and "spectral signature" are used herein
interchangeably to define a set of data corresponding to a document or a set
of
documents. In particular, a broadband spectrum of reflected light from a
document,
or an area of a document, for example, can be referred to as a "spectral
signature" for
the document.
Refernng now to the process flow diagram of Figure 1, an embodiment
of the method of the present invention is provided. After a document is
provided, the
method begins by providing a broadband light source which is preferably
embodied as
a broadband tungsten halogen lamp. A conventional tungsten halogen lamp
provides
light with wavelengths in the approximate range from 320 nm to 750 nm. The
lamp
can be conventionally regulated to provide a relatively consistent
illumination level
1 S by removing high frequency light intensity fluctuations. In step 102, at
least a portion
of the document is presented for illumination by the broadband light source
which
produces reflected light from the document. In step 104, the method includes
collecting the reflected light such as by use of an optical fiber with a
collection lens.
In one embodiment, the reflected light is focused onto an optical fiber
in step 106 and then is transmitted to an optic module where it exits the
fiber through
a pinhole or aperture provided in the end of the optical fiber. The pinhole is
located in
the proximity of the focal point of a collimating lens, which cooperates with
a
diffraction grating to form a Littrow spectrograph. The lens of this method
collimates
the polychromatic reflected light exiting the pinhole in step 108. The light
is then
diffracted into its spectral colors by using a device such as the diffraction
grating in
step 110.
Referring again to Figure 1, the now diffracted, polychromatic
reflected light is then passed back through the colliminating lens, which now
acts as a
focusing lens to focus the reflected wavelengths of light. Then, in step 112,
this
focused light is transmitted to a photosensor such as a CCD photosensor chip
by the
collimating lens. The sensor chip contains a linear photodiode array that is
arranged
such that each photodiode captures a portion of the wavelengths in the
spectral
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composition of the reflected light. The exposure or integration period of the
sensor
chip can be controlled with a microcontroller and it may be varied from
document
sample to sample to allow for varied ranges of brightness in the documents
measured.
The method also includes converting the reflected light into an electrical
signal or
signals of that light.
Once the integration period expires, the microcontroller obtains the
signal of each photodiode in step 114. During this process, each signal is
clocked out
of the photodiode sensor chip in step 114, passed through an operational
amplifier
circuit for scaling, and then digitized such as with an analog to digital
converter in
step 116. The method next provides for converting the digitized voltages of
the
reflected light into an array in step 118. Once inside the microcontroller's
memory,
the array may be normalized and compared to a previously stored target array
in step
120 with a matching function that produces a matching value, preferably
embodied as
a hit quality index or HQI value. An array which is obtained or stored may be
1 S considered to be a spectral signature for a tested document.
Refernng again to Figure 1, step 120 of the method also involves
comparing the spectral signature to a previously stored target value to
determine if the
spectral signature is within acceptable limits of authenticity. If its value
is within
these acceptable limits, which may be obtained during field programming of an
authentic document, the sample is classified as authentic and the method may
then
output the result of the comparison in step 122. This output may be embodied
by the
microcontroller indicating authenticity such as by turning on a green light
emitting
diode. Conversely, if the test document is not within acceptable limits, then
a red
light emitting diode, for example, may be activated as notification to the
user of
document inauthenticity. Although, in the scope of the present invention,
output of
results can also include visual or audible notification to a user and can
provide storage
of information on digital or magnetic media. The transmission of data may
occur
with or without visual enhancement, such as by display of the data in a
graphical
format on an electronic monitor.
In the method of the present invention, the documents to be measured
may be of varying brightness levels from general wear, washing, soiling or
fading.
Subtle variations in light intensity tend to influence the magnitude of the
sampled
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spectral data and affect the comparison functions. The method of the present
invention minimizes the effect of these variations in intensity. To account
for these
variations, mathematical operations are applied to the array of the spectral
signature to
normalize the array for absolute magnitude before the authentication process
is
completed. This normalized array may be considered a spectral signature for
that
document. In production, care must be exercised to utilize spectrally
consistent
colorants during the document manufacturing process to ensure consistent color
signatures in the documents.
A mathematical matching function, which can be designated a Hit
Quality Index (HQI), is used to compare a sampled array to a target or stored
array.
The HQI function is a formula which has a limit approaching zero in proportion
to the
degree of correspondence between a sampled curve and a target curve. In the
method
of the present invention, a HQI function is a measurement of authenticity or
"fitness"
of a spectral signature with respect to a trained, previously programmed,
target
spectral signature. Comparison between these measured HQI results for a
document
to be analyzed and a previously measured spectral signature permits
authentication.
The method measures differences between a sample set of data and a target set
of data
and judges document authenticity based on a set of upper and lower limits
derived
from the standard deviation of the training set used to develop a given target
spectral
signature.
In the preferred embodiment, statistical analysis of a plurality of
original documents and a plurality of facsimile documents can permit suitable
matching indicators such as the HQI to be determined. Mathematical algorithms
for
those indicators can then be developed for use by an apparatus employing this
method
in determining authenticity of a document in question. For example, it will be
appreciated that an HQI may be provided as a weighted function to account for
areas
of the spectrum which are deemed more experimentally important than other
areas for
purposes of document authentication.
In operation, the method of the present invention procures a spectral
signature by sampling spectral data obtained from illuminating a portion of a
document. The spectral data from the photosensor, which may be a photodiode
sensor chip, is digitized. It may result in an array of n bytes, or preferably
128 bytes,
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with values ranging from 0 through 127. These array elements are zero indexed
such
that if R represents the array, Ro contains the spectral response from the
highest
frequency, preferably in the range of about 800 nm, focused onto the sensor
chip, and
R12~ contains the spectral response from the lowest frequency, preferably in
the range
of about 300 nm, focused on the chip. It will be appreciated that the spectral
range
and the number of array elements may be changed without departing from the
teaching and scope of the present invention.
It will be appreciated that the scope of the present invention includes
other areas of the spectrum. For example, a silicon detector operates from
about 200
to 1,000 nm; GaAs detectors operate from about 700 nm to 3,000 nm; and,
pyroelectric detectors operate from about 1,000 nm to 15,000 nm. It can
therefore be
understood that various optical components can be selected in the present
invention to
accommodate different frequency ranges.
Once the spectral data is obtained, the method optionally employs a
1 S step for discarding the user-determined "noisy" parts of the spectrum to
prevent
excessive signature variation and to provide a "clipped" or truncated
signature.
Elements of a CCD photosensor array, for example, that are exposed to
relatively low
levels of light tend to acquire a relatively random and noisy signal. To
resist this
"dark" noise from causing excessive variation in the spectral signatures, the
preferred
method of the present invention discards spectral data that are less than a
certain value
as follows:
C; = max (R; - f, 0) (Eq. 1 )
where C is the resulting clipped signature and where iE[0,1,...,127] is the
element of
the sensor chip, R is the spectral data sampled from the sensor chip, and f is
the
spectral noise floor value which may be predetermined and selected by a user.
This
noise floor value is user selected in the method to allow for a wide array of
varying
samples to be examined.
The next step employed to convert the spectral data into a spectral
signature is normalizing the data. Subtle variations in light intensity or
luminance
tend to influence the magnitude of the sampled spectral data. These variations
in
luminance can be attributed to physical wear and tear experienced over the
lifetime of
the document or documents, such as from soiling, washing, or general fading.
It is an
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object of the present invention to minimize the effect of these fluctuations
in inteirsity,
while preserving the integrity of the spectral signature. To accomplish
normalizing
the spectral signature, the array of spectral signature data may be normalized
as
follows:
nC~
N. _
1 127
C
j=0
(Eq. 2)
where n is the integer number of array elements, where N is the resulting
normalized
spectral signature, where iE[0,1,...,127], and where C is the clipped
signature resulting
from a previous step in the method.
To authenticate a spectral signature, the method of the present
invention obtains and stores target special signatures against which sampled
spectral
signatures are compared. The method also provides acceptable tolerance limits,
obtained from document testing, within which a sampled spectral signature may
vary
and still be considered authentic when compared to its corresponding target
signature.
To create a target or authentic spectral signature the method may analyze
signatures
of several known valid documents of the quality of the documents to be sampled
and
average those signatures into a composite spectral signature for the document
type:
n
SiJ
- j=1
T.-
1
n
(Eq. 3)
where iE[0,1,...,127], S;j is element i of training signature j, n is the
number of
signatures in the training set, and T is the resulting target signature. It
will be
appreciated that the "N" and "S" values described in the preceding two
equations are
interchangeable in their application to the present invention.
The training set is a representative sample of documents likely to be
encountered in commercial application of the method of the present invention.
The
standard deviation of the training set is used to determine the acceptance
deviation or
acceptable tolerance limits in the samples being tested. To qualify the
variation in the
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training set, the standard deviation of each signature element across the
training set is
computed, and the result summated:
n
2
127 ~ ~'sij ) n 2
HQISD=~ '=1 - ~ Sii
i=0 n '=1
(Eq. 4)
where S~ is element i of training signature j, and n is the number of
signatures in the
training set. This value is called the HQISD since it is mathematically
equivalent to
the standard deviation of the HQI's of the training set signatures.
When a signature is to be tested, the HQISD for the document type is
multiplied by a tolerance limit factor to determine the greatest HQI that a
sample
array can have and still be considered valid. The user may set this multiplier
depending on the tolerances of the production process and the degree to which
the
sample set represents documents likely to be encountered in the commercial
application of the device. If the target signature's HQI value is less than
the product
of this multiplier and the HQISD, then the sample is considered authentic.
Thus, a function called a hit quality index (HQI) may be used to
1 S compare a spectral signature to a target signature. An HQI is a
measurement of
"fitness" of a spectral signature with respect to a trained target signature.
The
calculation for the HQI implemented in this embodiment involves a subtraction
of the
respective array elements of the sampled signature from the target signature
to obtain
difference vector elements, and summation of the absolute values of the
resulting
difference vector elements. Therefore, if T is the target signature, and S is
the sample
being tested, then
127
HQI =~ I T -St
i=o
(Eq. 5)
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As discussed previously, if specific areas of the sampled spectrum are deemed
more
experimentally important than others, then a weighted summation could be
employed
for calculating the HQI value. For example, the "weighting function" can be an
array
of values multiplied by the spectral signature array, such that,
iz~
Hpl=~ W ~T -St ~
r=o
(Eq. 6)
where W; is a weighting vector with numbers less than one corresponding with
numbers in a sampled array which are deemed less relevant and numbers greater
than
one corresponding to numbers in a sampled array which are deemed more
relevant.
For example, a portion of a sample weighting function can be expressed as
follows:
W; = f 0.5, 0.5, 1, 1, 0.5, 0.5, 1.2, 1.2 . . .~
It can be understood that use of a weighting function will be driven by
factors such as
the type of light source employed and the quality of documents which are
tested.
With reference to Figures 2 through 4, the following examples are
intended to illustrate several embodiments and uses of the present invention.
These
examples are not intended to limit the scope of the present invention.
Table I - Tabulation of Analysis of Figure 2
Acceptable # of HQISD's (Acceptance Threshold): 3.00
Target Signature HQISD: 0.00585046
Acceptable Limit: 0.01755139
Curve H I # of HOISD's Out ut
A 0.00715536 1.22 Authentic
B 0.09706872 16.59 Inauthentic
C 0.10568740 18.06 Inauthentic
D 0.21941390 37.50 Inauthentic
E 0.1899286 32.46 Inauthentic
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As an illustrative example, refernng now to Figure 2 depicted herein, a series
of spectral signature curves A, B, C, D and E can be graphically represented
to demonstrate
analysis of a document sample to determine its authenticity. These spectral
signatures are
plotted as Intensity values (unitless) versus each data point obtained from a
tested document
( 0 - 127) for the purpose of this example). As shown in Figure 2, the Target
Curve A is the
spectral signature curve representation of a previously stored target
signature generated by
the method of the present invention. It will be understood that the Intensity
values to be
considered authentic, the graphical representation of a tested document must
sufficiently
map to the Target Curve A. By contrast, the curves B, C, D and E are not
authentic and do
not sufficiently map to the Target Curve A to be considered authentic.
Referring again to Table I in conjunction with Figure 2, an example of a
tabular representation of the document analysis is presented. In this example,
the method of
the present invention provides for establishing an HQISD value for the target
spectral
signature of 0.00585046, which is calculated during the programming and
storage of the
target spectral signature. A threshold value of 3.00 is multiplied by the
target signature
HQISD to provide a range having an upper limit which provides the acceptable
number of
standard deviations within which a tested or sampled spectral signature HQI
value may fall
2 0 for a determination of a document authenticity. In this example, the
acceptable limit is
calculated to be 0.01755139. Therefore, only "Authentic" test data which has
an HQI of
0.00715536 falls within the range of the required 3 HQISD's established for
acceptance by
the Target Curve A spectral signature.
In another embodiment of the present invention, an apparatus for verifying
2 5 the authenticity of a document is provided. It will be appreciated that
the apparatus
described herein is illustrative of a typical embodiment of the method of the
present
invention and that certain conventional components of the apparatus may be
exchanged
with other suitable components.
Referring now to Figures 3 and 4, the apparatus 1 of the present invention is
3 0 shown with an enclosure 2 having a window 4 or other conventional
transparent opening
formed therein. The enclosure 2 is provided as a generally box-shaped metal
enclosure
which is suitable for containing the components of the
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apparatus 1 of the present invention. At least a portion of a document 6 is
placed over
the window 4 to permit a broadband light source 8, which can be provided as a
tungsten halogen lamp, for example, to illuminate the portion of the document
6
placed on the window 4. It will be understood that the percentage of the
document
surface will be subject to the discretion of the user. The amount of the
document
illuminated will depend on factors such as the type of document analyzed and
the
portion of the document surface required to present a representative and valid
sample
for testing. The document 6 can be conventionally indexed in conjunction with
the
apparatus 1 to position the desired portion of the document 6 to be analyzed
over the
window 4.
The light source 8 transmits light wavelengths TL to the document 6.
A collection lens 10 and an optical fiber 12 are provided to collect and
transmit
reflected light RL emanating from the document 6. An aperture or pinhole 14 is
positioned at an end 15 of the optical fiber 12 and is also adjacent to the
focal point
FP of a collimating lens 16. The collimating lens 16 receives light PL from
the
pinhole 14 and then collimates the light PL into collimated light CL. The
collimated
light CL is then converted into diffracted light DL by a diffraction grating
18 or
another suitable diffraction device. It will be appreciated that a
conventional
refraction technique could also be employed in lieu of this diffraction
grating 18. It
will also be appreciated that optical components of the present invention can
be
combined into an optic module 19 as shown in Figure 4.
The collimating lens 16 now acts as a focusing lens to focus the
diffracted light DL into focused light FL and transfer the focused light FL to
a sensor
chip 20, which may be embodied as a CCD photosensor chip. The focused light FL
can be separately grouped into longer wavelength light and shorter wavelength
light
as it impinges on the sensor chip 20. The focused light wavelengths FL are
converted
to an electrical signal or signals, which can be voltages, and stored by the
sensor chip
20. The signals stored on the sensor chip 20 therefore represent different
wavelengths
of the focused light. The signals are then clocked out of the sensor chip 20
and
processed as analog signals AS. The signals are clocked out of the sensor chip
by an
operative connection 21 with a conventional microprocessor 26 or other
suitable
microcontroller. The microcontroller 26 is also operatively associated with
the sensor
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chip 20 to permit adjustment of the exposure time for the focused light FL
impinging
on the sensor chip 20.
The analog signals AS are then conditioned for further analysis such as
by processing the signals AS through an amplifier 22. The output of the
amplifier 22
feeds the signals AS into a conventional analog-to-digital converter 24 to
generate
digital signals DS which correspond to the analog signals AS. A
microcontroller 26
or other suitable, conventional microprocessor is employed in conjunction with
the
apparatus 1 to receive and process the digital signals DS. The digital signals
DS are
then processed by the microcontroller 26 consistent with the method of the
present
invention previously discussed. It will be appreciated that since the software
employed in the preferred practice of the present invention may be readily
programmed and used by one skilled in the art, a detailed description of this
software
is deemed unnecessary.
In addition, a conventional switching system 28 is employed to change
the various functions of the apparatus of the present invention. The apparatus
1 is
powered by a conventional power supply 30 coupled to a power cord 32.
Optionally, a user may be notified of the authenticity or other
information about the digital signals DS by a pair of lights 28,30. For
example, the
light 28 may be a red light which indicates an inauthentic document has been
tested
and detected. In addition, the light 30 may be a green light which notifies
the user
that an authentic document has been presented to the apparatus 1 for testing.
The following examples are intended to represent particular aspects of
the operation of the method and apparatus of the present invention. It will be
appreciated that these examples are not intended to limit the scope of the
invention,
but rather teach a use of the method and apparatus to one skilled in the art.
EXAMPLE 1 - OPERATION
Normal operation of a device employing the method of the present invention,
which is known as a "DFS" device or a "Document For Sure" device, does not
require
the device to be connected to a personal computer or other microprocessing
apparatus.
The DFS device can undergo new programming and verification duties as a
standalone unit. The situation may arise, however, where the user desires to
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the operating parameters of the device or receive extended information
regarding the
spectral signatures being sampled and stored. To address these needs, the
method and
apparatus of the present invention can provide a serial communication protocol
and
interface by which a computer or other conventional microcontroller may
communicate with and control the DFS device.
A user may issue commands to the DFS device using a suitable,
conventional device that supports standard asynchronous serial communication,
i.e., a
standard computer serial port. All commands sent to the DFS device can be in
lower
case ASCII, and are separated from their parameters by one or more spaces. A
listing
of commands which are used to communicate with the microcontroller can be seen
in
Table II (below):
Table II - Microcontroller Commands
Command Parameter Description
Serialon (none) Tells the DFS device to report
spectral
signatures as they are acquired.
Serialoff (none) Tells the DFS device not to
report spectral
signatures as they are acquired.
Setfloor Noise floor Sets the noise floor value
for testing
samples. Value from 0-255.
Default of
50.
Getfloor (none) Displays the current noise
floor value.
Setthresh Threshold Sets the acceptance threshold
in number
of standard deviations for
test samples.
Value of 0 or higher. Default
of 3.
Getthresh (none) Displays the current acceptance
threshold.
Settarget (none) Sets the current target spectral
signature
and the HQISD of the signature.
Gettarget (none) Gets the current target spectral
signature
and the HQISD of the signature.
Sample (none) Acquires a spectral signature
or array.
(May be a "sample" button.)
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The DFS device can be instructed to transmit the spectral signatures to
the user as the signatures are sampled. This permits the user to create graphs
of the
spectral signatures as acquired. This feature can be enabled by sending the
"serialon"
command. Once it is enabled, the DFS device sends each sampled spectral
signature
over the serial port until the DFS device is reset or the "serialoff ' command
is issued.
This feature can be disabled by default when the DFS device is reset so that
the DFS
device can operate without being attached to a computer.
There are two operating parameters that can be changed using the
serial protocol: the noise floor value which is changed using the "setfloor"
command,
and the acceptance threshold which is set using the "setthresh" command. The
noise
floor value is the intensity value below which the noise level is still be
considered too
great for a portion of the photosensor to contain useful information. The
acceptance
threshold is the number of standard deviations of the HQI of the target
spectral
signature by which tested spectral signature samples can differ from their
stored
spectral signature counterparts and still be considered valid.
The user can also query the DFS device for several different types of
information. The "getthresh" and "getfloor" commands return the respective
operating parameters which they represent as set by the user as shown in Table
II. In
addition, the "gettarget" command returns the target spectral signature
against which
samples are being compared, and the standard deviation of the HQI's used in
subsequent calculations for comparison. The "settarget" command permits
previously
trained spectral signatures which may have been developed and stored on a
device
such as a computer to be received by the DFS device.
The "sample" command may be sent instead of pressing, for example,
a "sample" button on the apparatus of the present invention. The user may also
automate sample acquisition to create continuous spectral signature graphs,
for
example, of the individual sampled document spectral signatures. The function
of the
"sample" command may be dependent on the position of a "verification/training"
switch which can be employed as part of the apparatus of the present
invention.
The DFS device includes two modes of operation: training and
verification. In training mode, the user programs the DFS device to recognize
and
store a target spectral signature by presenting multiple samples to the
device. In
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verification mode, the user can test a sample document against the spectral
signature
for the corresponding document type for which the DFS device has been trained.
EXAMPLE 2 - TRAINING MODE
Before the DFS device can test and establish a spectral signature for a
specific sample, it is first programmed to recognize the spectral signature of
that
sample. With respect to the method and apparatus of the present invention, the
training or programming process includes several steps. First, the user
switches the
DFS device into training mode. Next, the user positions a programming sample
over
the window of the device, presses the sample button and waits to view a green
light.
The positioning, pressing the sample button, and viewing the green light steps
are
then repeated for analysis of additional samples to be programmed. When all
desired
documents have been sampled, the user can switch the DFS device to
verification
mode. Finally, the user presses the sample button to finalize programming and
to
make the programmed signature available for testing purposes.
The DFS device then analyzes a sample in verification mode at the end
of the programming process; this first sample in verification mode directs the
DFS
device to finalize programming. The verification mode is discussed hereinafter
in
further detail. It is also at this time that the mean and standard deviation
of the
training set spectral signatures are calculated.
It will be appreciated that a sampled spectral signature must consist of
at least two measurements, preferably more than two, for training and storage
purposes. It will also be appreciated that if a different HQI function is
employed, then
this measurement plurality requirement may not be necessary. This is because
verification, or the determination of document authenticity in the preferred
embodiment of the present invention, is a function of the standard deviation
of the
spectral signatures which are part of the comparison process. If the spectral
signature
consists of only one measurement, the standard deviation will be zero which
will
preclude any subsequently tested document from being accurately determined as
authentic or inauthentic. A preferred spectral signature consists of several
documents
of the same kind and degree of variation as the documents that are to be
tested and
analyzed.
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EXAMPLE 3 - VERIFICATION MODE
Once the DFS device has been programmed, it can be used to check
the spectral signature of a test document against its stored target spectral
signature
counterpart. The verification process involves the first step of switching the
DFS
device into verification mode. Next, the user positions the sample document to
be
verified over an opening such as a window of the device. Finally, the user
presses a
"sample" button, for example, and can expect output of the inauthenticity or
authenticity of the document in the form of a visual display such as a red or
green
light, for example, or the output can be stored to magnetic or digital media.
For visual notification of the output, a red light can indicate that the
sampled spectral signature lies outside the specified acceptable limits or
tolerance and
a green light can indicate that the signature lies within the acceptable
limits. The
acceptable limits are expressed as a function of the standard deviations of
the
individual programmed target spectral signature when employing the preferred
HQI
function to determine document authenticity. As previously discussed, the
acceptable
limits may be programmed using a serial communication protocol.
It will therefore be appreciated that the present invention provides a
document analysis which utilizes a broad band of wavelengths to provide a more
thorough and more reliable determination of document authenticity. The present
invention also provides an apparatus for analyzing documents which can be
produced
at an economical cost. The document analysis method and apparatus disclosed
herein
also advantageously reduce the inherent variation introduced into the analysis
by
soiled or faded documents which are tested.
While specific embodiments of the invention have been disclosed, it
will be appreciated by those skilled in the art that various modifications and
alterations to those details could be developed in light of the overall
teachings of the
disclosure. Accordingly, the particular arrangements disclosed are meant to be
illustrative only and not limiting as to the scope of the invention which is
to be given
the full breadth of the appended claims and any and all equivalents thereof.
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